Add Example of Bug Due to Mutation in "Dangers of Mutability"

[rmorshea]

Include something like this example in the "Dangers of Mutability" docs.

[rmorshea]

Gonna push doc issues to later since we're thinking of revamping docs anyway.

[Archmonger]

I'm planning on handling all existing docs issues in the revamp

[rmorshea]

Can you add "closes #XXX" for the issues you plan to address?

[Archmonger]

Added to #863

[Archmonger]

I also propose we do not assign docs changes to version milestones anymore.

I don't think it makes much sense since versions are source code specific.

Maybe a GitHub milestone for "Docs Changes" is needed? But that might be pointless, may as well just filter using the type: docs tag.

[rmorshea]

Sounds good to me.